1. Field of the Invention
The present invention relates to a seat back arrangement for a vehicular seat. More specifically the present invention relates to a seat back arrangement for a vehicular seat in which a support structure for supporting the lower back or lumbar section of the seat occupant is adjustable so as to improve the comfort of the occupant and to decrease fatigue during long drives.
2. Description of the Prior art
One example of a conventional prior art lumbar support device is shown in Japanese Utility Model First Provisional Publication No. 60-137850.
In this device, in order to provide additional support for the lumbar section of a vehicular seat occupant, an inflatable pneumatic cushion is provided so as to be mounted at an inside front position of the vehicular seat. The pneumatic cushion is disposed at the portion of a seat back which supports the lower back or lumbar portion of the seat occupant. By adjusting the pressure of the air in the pneumatic cushion, it is possible to adjust the firmness and, in effect, the contour of the portion of the vehicular seat which provides the support to the lower back of the vehicular seat occupant.
The above described pneumatic seat cushion has various disadvantages, however. One disadvantage is that it is difficult to adjust the air pressure in the pneumatic cushion to a pressure which is comfortable for the seat occupant while still providing enough support for the lower back portion of the vehicular seat occupant to prevent fatigue.
Another disadvantage of the above pneumatic cushion is that it is an unsightly and troublesome addition to the front of the seat.
Still another disadvantage of the above pneumatic seat cushion is that, since it is not integral with the seat back, when it is inflated so as to provide a degree of lower back support which decrease fatigue of the seat occupant it tends to cause the seat occupant the uncomfortable sensation that there is a foreign body interposed between the front of the seat and the occupant's back.